This invention relates to scraper bars for conveyor belting and the like and more particularly to scraper bars having a layer of hard abrasion-resistant pellets embedded in an elastomer.
When conveyor belting is used to transport granular material, it is necessary to wipe the conveyor belting surface with a blade or the like to remove any such material which may adhere to the belting. Such blades, called scraper bars, have been used for many years and have been formed from various materials, including various rubbers and urethanes.
To get good scraping or cleaning action, the scraper bar must bear directly against the conveyor belting. If the scraper bar bears properly, it quickly wears out. As an example, a rubber scraper bar (Hardness 60, Shore A) forming part of a plow removing bauxite was seen to wear by 1/8" in a 12-hour period when it was sufficiently pressed to the conveyor belting to ensure good scraping action. While urethane scraper bars do improve wear resistance, they do not always last sufficiently longer that their extra cost can be justified by the user.
Recently, to overcome this wear problem, there has been introduced in the market scraper bars consisting of a layer of hard abrasion-resistant ceramic pellets embedded in a cast urethane or other elastomer to form an elastomer/pellet matrix. An additional layer of elastomer is cast to the matrixed layer to provide a place for attaching the scraper bar to a support when it is in service. These pellets are formed from a very hard, abrasion-resistant material such as ceramic, which allows long term wear without injury to the conveyor belting.
During manufacture of such a scraper bar, a mold made of aluminum, steel or other suitable rigid material is utilized. A layer of freshly mixed elastomer, such as urethane polymer, is cast directly into the bottom of the mold and a predetermined quantity of suitable pellets such as those formed from a ceramic material are added. The pellets should be treated with an adhesive bonding agent to fix them firmly in the elastomer. The pellets are mixed intimately with the elastomer, and the matrixed layer thus formed is then leveled before the elastomer begins to gel. The remainder of the mold is then filled with a freshly mixed elastomer formulation and the entire bar is cured at an elevated temperature. After curing, the finished scraper bar is demolded.
When a scraper bar is made in this fashion and allowed to cool and equilibrate for several days, the scraper bar thus formed bows. The bowing is particularly noticeable in scraper bars longer than twelve inches in length. The bowing reduces the amount of contact between the scraper bar and the conveyor belting surface being cleaned and thus renders scraper bars greater than twelve inches unacceptable for use in cleaning conveyor belting. The bowing can be overcome to a certain extent by applying pressure on the extreme top ends of the scraper bar. This technique results in the application of extreme force to the scraper bar with resulting excessive and uneven wear patterns.